1. Related Applications
There are no applications related hereto heretofore filed in this or any foreign country.
2. Field of Invention
Our invention relates to self-contained, medium energy gamma irradiators and more particularly to such an irradiator that is portable, self-contained, and moves a radiation source vertically downwardly for use.
3. Description of Prior Art
The irradiation of food for preservation or other purposes has been known for some time. Commercial irradiation started at least as early as the 1950's and research on the subject throughout the world has become increasingly intensive to the present day. A large portion of the technology in this field has developed in the recent past and outside the United States because of a much less restrictive environment elsewhere than in the United States, where radiation has largely been looked upon by governmental authorities as an adulteration of food by additives and not as a beneficial or conservation process.
Attitudes have changed with the passage of time and the pressure of economics, however, and radiation is coming to be used in more and various food processes such as sterilization or pasteurization without raising the temperature of sealed food packs, improving processability of foods such as by requiring shorter cooking time, initiation and acceleration of maturity as in the aging of cognac, retarding food ripening, pest control as with papayas, inhibition of germination as in potatoes and onions, and in combination with other processes common to the food processing arts to enhance the activity and results of such other processes. The potential of such applications presents an almost boundless horizon.
Unfortunately, the apparatus for irradiation of food stuffs has remained in the same primitive state as the process itself. Most known apparatus has been extremely expensive because not only of the regulatory environment in which it exists but also by reason of lack of research, knowledge and appropriate engineering ingenuity. The instant invention seeks to provide a new and novel member of the class of commercial irradiators for food stuffs which overcomes many of the disadvantages of those devices as heretofore known.
Commonly in the past, irradiation of food has been carried out by cobalt-60 energy sources which produce gamma radiation of relatively high energy. This source probably gained its popularity because of its availability. In the recent past, however, cesium-137, which occurs as a byproduct of uranium fission in nuclear power reactors, has become more available and provides a somewhat lower energy source of gamma radiation. The economics of the two materials are substantially similar, as in general most radiation sources are priced proportionally to their intensity of radiation and though that intensity is higher with cobalt-60, that material's life span is also less, approximately 5.2 years in half-life, while cesium-137 has a half-life of 30 years. The lower energy of the later radiation source, however, does not require such extensive shielding as the cobalt-60 source and allows a better and more efficient design for a portable irradiator of the type of the instant invention.
In general, known food irradiators have been massive installations with permanent or semi-permanent radiation sources to conform to the previously described philosophies and to some degree because of the dictates of the high energy radiation sources which they embodied. Our invention, in contra-distinction, provides a relatively small portable device that is entirely self-contained. This offers substantial economic advantage over the prior art devices in that our invention may be used as its own transport container without further shielding or modiiication. This allows the ready use of one or more radiation sources in a particular project for a limited period of time with subsequent removal and transport between various irradiation sites so that one or a group of irradiators may be used at one site for a particular crop or product and thereafter may be readily moved to another site for processing of other material as desired. This self-contained, transportable feature of our irradiator also materially aids the loading and unloading of various radiation sources from the device when this should be necessary.
The design of our irradiator also allows its convenient use at various locations with seasonal crops. With massive irradiators of the prior art, if such a facility were to be used for more than one product, a secondary product commonly would have to be transported to the facility. With our invention, since the irradiator unit itself is relatively small and self-contained, it may be quite conveniently moved at different times to various local processing facilities to process materials then and there available. This materially lowers the overall cost of processing as it minimizes transportation requirements and maximizes the period of facility usage.
Our invention, again, uses the lower energy source of cesium-137 as opposed to the higher energy cobalt-60, commonly used heretofore in most irradiation facilities. Though the economics of the two materials are about the same, the lower energy material provides quite sufficient energy for food irradiation but yet requires less shielding to allow use of a smaller, more conveniently transportable container. The cesium-137 is generally available and merchandised.
A further advantage accrues from the portable and transportable nature of our irradiator. The device may be transported to an equipped facility for radiation source loading to avoid the hazardous operations of loading and the transportation of radiation sources.
Our irradiator body is configured to expose a radiation element for use by moving that element downwardly, and this allows a radiation facility configuration such that our device is positioned above a chamber wherein radiation takes place. This configuration allows the use of tunnel-type irradiation facilities which are most convenient and cost effective, as they allow use of the ground as a shielding element and do not require the use of water, either as a shielding element or a storage medium. This structural feature materially lessens the overall cost of irradiation facilities whereat our irradiator is to be used, so that a plurality of such facilities may be economically provided for use at different times in different locations, whereas with the larger, more massive and costly facilities of the prior art this was not possible.
The small size of our irradiator and the configuration of the facility in which it is used are both conducive to allowing the use of a plurality of irradiators at one site, if required. This feature also allows additional irradiators to be added at a facility to speed up processing at peak periods. The prior art irradiators generally did not allow this type of activity as their radiation sources were relatively fixed and generally could not be well or economically modified to add additional radiators, either because of the difficulty in providing them, the problems that would arise from shielding, the physical limitations of the space in the facility itself or similar causes.
Our irradiator provides a small, modular unit that, by its design, is of relatively low cost as compared to prior apparatus. Similarly the facility in which irradiation is had is so positioned and configured as to provide a relatively low cost per unit of product handled, as compared with prior facilities. These two elements combine to allow product irradiation at a substantially lower cost than has heretofore been had. Our irradiator also provides at least a substantial part of its on-site shielding and thus lowers the shielding requirements of a facility at which it is used.
Our invention resides not in any single structural feature or function per se, but rather in the synergistic combination of all features and the functions necessarily flowing therefrom to distinguish it from the prior art, either individually or in any combination of its elements.